Method of producing a negative by reversal



Dec. 18, 1934. Q R HARRISON 1,984,580

METHOD OF PRODUCING A NEGATIVE BY lEVERSAL Filed Sept. 9, 1929 INVENTOR Patented Dec. 18, 1934 UNITED STATES PATENT. OFFICE METHOD OF PRODUCING A NEGATIVE BY REVERSAL 3 Claims.

This invention relates to an improved method of making a light resist film or plate, or a negative by reversal, upon a. fluid-repellent base, either transparent or translucent, from which 5 prints such as half-tones and the like can be made, and has for an important object the production of such negatives in either transparent or translucent form with either direct or reflected light, in such manner that although very quickly, cheaply and simply producible, the negative follows with great fidelity even the most minute printed markings, such as those of a very fine half-tone screen.

Other objects and advantages will be apparent from the following description, wherein reference is made to the accompanying drawing illustrating preferred embodiments of my invention, and wherein similar reference characters designate similar parts throughout the several views.

In the drawing:

Figures 1 and 2 represent respectively a plan and an edge or sectional view greatly enlarged, and exaggerated diagrammatically showing successively from left to right the alterations produced upon a film or plate by the progressive steps comprised in the production of a negative in accordance with my preferred process.

Figures 3 to 7 inclusive are views similar to Figure 2 of various modifications; and

Figure 8 is a plan view similar to Figure 1, but reversed, being intended to bring out the results produced upon a negative by carrying out my process.

As far as the design is concerned, the one here selected for purposes of illustration is purposely of supreme simplicity, though it is obvious that the process steps here to be described are applicable to any design selected, such as the dots of a half-tone or the like.

The first step of the process consists in the drawing or placing by printing or other suitable means of a chemical resist design, that is one resistant to certain solvents, upon a transparent or translucent base of celluloid, gelatin or the like. The imprinted chemically resistant design is just the opposite of the ultimately desired negative design, and may be printed or otherwise applied with a greasy ink or suitably resistant medium such as petroleum jelly, paraffin or the like. The character thereof, whatever the medium chosen, is such that the subsequently applied light-resisting material will not materially adhere to or affect the same.

If the chemical resist design be a transfer, or

liable to be weak as to chemical resistance, then it is preferable to strengthen it by applying to its sticky or greasy surface an additional chemical-resisting substance, which adheres in quantities to this design surface only. This can be done by dusting, rubbing on, or by other means applying a powdery substance, such as finely powdered dry wax, or its equivalent.

It is then preferable to clean the surface of the base between the applied design sections, and if desired to etch or slightly impair the surface, so as to produce in it minute irregularities. For this purpose I have found a dilute chromic acid solution suitable if a base of ordinary flexible film material, celluloid, or gelatine is used, though I do not desire to be understood as restricting myself thereto. It will be understood that the chromic acid wash will not affect the chemical resist design.

After preferably, though not necessarily, again washing the base, I smear on the design side thereof a chemical which preferably impregnates the base, although a portion may remain substantially at the surface, and which has a tendency to sublime or evaporate out or again emerge in any other fashion if left undisturbed. It has been my experience that iodine, either in a solution or as a gas, is best for this purpose, although other media, some of which thus far in my experience have not functioned as satisfactorily as iodine, may be used.

After again preferably washing the base, I smear the design side thereof with another (ordinarily liquid) material such as methyl violet die, which does not penetrate the base, but does combine with a part of the already applied iodine at the surface of the base as the iodine emerges. The presence of sufiicient iodine at the surface at the time its reaction with the dye is wanted is assured by the tendency of the iodine to emerge. Such combination of course only takes place in the spaces between the previously applied chemical resisting sections. The iodine and dye thus combined form on the base surface a comparatively insoluble light resist. The negative is made with the first application of dye, and the addition of iodine the second time is optional and intensifying rather than essential. Whether this dye or some equivalent substance is used, it should be of such a character that little or no soluble chemical remains at the end of this step, and to assure this I preferably again smear the exposed or nonresistant surface sections with iodine, removing the surplus by washing. The chemical resist is then dissolved or washed away, leaving the light-resist design.

The last application of iodine imparts -an outer surface or film to the light resist material which is even less soluble in certain chemicals than the portions within the light resist material. The thickness of this less soluble outer crust depends upon the strength of iodine or other substance that has been used, the length of time that it is left on the base. the surface character of the latter, and upon temperature conditions. By having this less soluble outer surface and a somewhat more soluble inner portion incorporated in the light resist, I provide simple means for altering the negative as regards light and shade effects by enabling application of another and preferably slow-acting solvent by which slow dissolving out of the inner substance of the light resist sections is possible thus undercutting the less soluble outer surface, the edge of which break and dissolve off as the undercutting dissolution progresses. This reduces the width of the light resist section and increases the spaces between correspondingly without materially reducing the opaqueness of the-light resist. It has been my experience that for effecting the dissolution of the inner substance when iodine and dye combination is used, alcohol is the best medium, though I do not desire to be understood as restricting myself thereto. If a more dense light resist is desired, the iodine-dye treatment or its equivalent may be repeated one or more times until the desired density is obtained.

If the chemical-resist design is sufficiently translucent for use, it of course need not heremoved, but if it was originally too light-resistant, or has become so during the process, it is necessary to remove it to complete the reversal, by melting, rubbing, dissolving or equivalent means. Subsequently thought-of changes from the initially intended design can easily be made before the negative is offered as complete and ready for use, by erasure or dissolution of selected sections of the light-resist material.

If a suitable film base has been used, the negative lies perfectly flat, without buckling or changing its size, since nothing has been added to or taken away from the base, the light-resist material being laid upon and parallel to the base and adhering to its surface.

Referring now to the exaggerated and more or less diagrammatic drawing, the wide and heavy black lines A shown in their illustrative intersectingplaninFigure 1,maybetakenas representing the initially applied protective or chemical resist design of greasy ink, paraflin, petroleum. jelly, or the like. As stated above, although shown as composed of lines, the design might and of course frequently would in practice be applied in the form of the dots composing a half-tone. In the figures the light squares B between lines represent those portions of the film desired to be darkened to enable production of the ultimate negative, from and through which prints may be made. The impregnation.

of the base by the application of iodine or its equivalent is represented by the small circles or globules C, in plan in Figures 1 and 8, and sectionally in the other figures. The dye element is represented by the small black dots D, placed within the iodine globules, to indicate their association. The compound of iodine and dye (although a surplus of dye remains solubly responsive to the action of suitable solvents),

is represented by the small circles with concentric dots E shown above the horizontal line which in Figure 2 represents the surface of the film or other base, and theiine sectioned portion Fin the next section of said figure represents the smeared iodine over the light resist, for changing the surface to a crust even less soluble under the action of chemical-resist solvents. The imprinted or otherwise applied design in greasy ink or the like is of course relatively soluble. Reference letter G designates the section in which is shown the finely effected dissolution, by the chemical resist solvent used for that purpose, of the greasy ink or the like, leavingthe light-resist material in place.

Reference H shows the breaking off of overhanging edges of the crust, resulting from application of a slowkv acting solvent for the lightresist, applied (if desired) to reduce the width of the light resistant portions with a corresponding increase in the size of the spaces therebetween. This does not materially decrease the opaqueness of the remaining light resist, and is of course an optional additional step.

With the removal by washing witha suitable solvent, as stated above, of the lines A of greasy ink or the like initially applied, there is left upon the surface of the base only the desired and selectively positioned dark and light areas which the process has produced by forming the light resistant sections in the described manner, and as previously stated printing therefrom in any desired manner may thereafter he proceeded with.

The modifications illustrated in the enlarged and diagrammatic edge, or sectional views of Figures 3-7 more or less symbolically, are designed to bring out other methods of chemically effecting changes in the unprotected portions of the base through the medium of a selection of chemicals which impair the exposed portions of thebasesurfacetothedegree ofmakingitmore absorbent before smearing. on the penetrating material, to form a comparatively insoluble chemical compound constituting a light resist. InFigureiitheobliquelinesJtei-be initial preparation of the surface of the base as by etching with chromic acid preparatory to the application of iodine or the like thereto, which penetrates the same, as indicated at K. The next step represented by character L, is the association therewith of the cbre, corresponding totheunitDofFigure 2, althoughinthiscase the dye penetrates the base. The combined dye and iodine form the light resist, which is embeddedinthebase,asshowninsectionll,after which,asshowninsectionsNandO,theprotective imprint may be removed to leave the light resist alone in a manner analagous to that described in connection with the first embodiment.

Figure4diifersfrom1 lgures2and3in thatitrepresentstheuseofanaturally absorbent base rather than a repellent base artificially roughened, to permit penetration of its surface. The dye and iodine applications are of such strength relatively to the base that the latter needs no preliminary impairment to enable their sinking thereinto in the manner illustrated as effected by preparatory impairment in Figure 3. The several steps willbereadilyunderstoodandwillbeseento be similar however.

Figure 5 similarly illustrates a case in which thesurfaceofthebasehasbeenchemicallyimpaired, and the light resist secured entirely by the staining of the places thus rendered absorbent, without the use of an iodine smear.

Figure 6 is illustrative of the completion of the negative through the medium of merely making the several smears of dye, iodine and the like adherent to the surface of the base, without their sinking into the body thereof. This figure, it will be noted, carries all of the symbolical globules above the surface line.

Figure 7 is illustrative of the employment of the process in such manner that reliance for the production of the ultimately desired light resist is placed upon the use of a stain alone, with an absorptive base, the small globules or circles there shown being equivalent in their function and method of association with the base to the globular characters C above described.

While it will be apparent that the illustratedembodiments of my invention herein disclosed are well calculated to adequately fulfill the objects and advantages primarily stated, it is to be understood that the invention is susceptible to variation, modification and change within the spirit and scope of the subjoined claims.

What I claim is:

l. The method of obtaining a light-resistant image on the surface of a selected base, which consists in first rendering those portions of the same whereon the ultimate lines of the image are located in reverse temporarily proof against the action of chemicals, then successively applying thereto a plurality of chemicals, one of which is impregnative of the unprotected portions of the base and. the other of which is combinative therewith and whose application results in the formation of a relatively insoluble light-resisting coating upon the unprotected portions of the base, and thereafter effecting the dissolution of the initially applied design lines.

2. The method of producing a negative by reversal from the initially applied markings, consisting in first applying the contourings desired to the surface of a permeable translucent base with a protective material which is insoluble in some solvents and soluble in others, applying to the unprotected surface portions a chemical adapted to first penetrate the base and then emerge, and then applying to said same surface portions a'liquid adapted to combine with the second applied penetrating material to form a light-resistant compound insoluble in a solvent for the protective material, and thereafter removing the protective contourings initially applied, thus leaving the corresponding portions of the base surface clear for the relatively unobstructed passage of light rays therethrough.

3. The method of producing a light resistant design upon an initially translucent base by chemical action, which consists in first positioning thereon the desired markings with a chemical-resist medium, subjecting those portions of the base not thus protected to the action of a halogen adapted to first penetrate and then emerge from the base, thereafter applying to such last named surface portions a material capable of combining with the halogen to form a relatively insoluble light-resist in the spaces be tween the chemical-resist, and then removing said chemical-resist.

RALPH H. HARRISON. 

